urn:nasa:pds:context:instrument:msi.near 1.0 1.7.0.0 Product_Context 2016-10-01 1.0 extracted metadata from PDS3 catalog and modified to comply with PDS4 Information Model urn:nasa:pds:context:instrument_host:spacecraft.near::1.0 instrument_to_instrument_host Hawkins, S. Edward III, E.H. Darlington, S.L. Murchie, K. Peacock, T.J. Harris, C.B. Hersman, M.J. Elko, D.T. Prendergast, B.W. Ballard, R.E. Gold, J. Veverka, and M.S. Robinson, Multi-spectral imager on the Near Earth Asteroid Rendezvous Mission, Space Science Reviews, 82, 31-100, 1997. reference.HAWKINSETAL1997 Murchie, S.L., M. Robinson, S.E. Hawkins III, A. Harch, P. Helfenstein, P. Thomas, K. Peacock, W. Owen, G. Heyler, P. Murphy, E.H. Darlington, A. Keeney, R. Gold, B. Clark, N. Izenberg, J.F. Bell III, W. Merline, J. Veverka, Icarus, Vol. 140, No. 1, 66-91, 1999. reference.MURCHIEETAL1999 MULTI-SPECTRAL IMAGER Imager not applicable not applicable This catalog file contains excerpts from: [HAWKINSETAL1997] Additional MSI instrument information can be found in: [MURCHIEETAL1999] Instrument Overview =================== The Multi-Spectral Imager (MSI) on the Near-Earth Asteroid Rendezvous (NEAR) spacecraft uses a five-element refractive optical telescope, has a field of view of 2.93 x 2.25 degrees, a focal length of 167.35 mm, and has a spatial resolution of 16.1 x 9.5 m at a range of 100 km. The spectral sensitivity of the instrument spans visible to near infrared wavelengths, and was designed to provide insight into the nature and fundamental properties of asteroids and comets. Seven narrow-band spectral filters were chosen to provide multicolor imaging and to make comparative studies with previous observations of S asteroids and measurements of the characteristic absorption in Fe minerals near 1 micron. An eighth filter with a much wider spectral passband will be used for optical navigation and for imaging faint objects, down to visual magnitude of +10.5. The camera has a fixed 1 Hz frame rate and the signal intensities are digitized to 12 bits. The detector, a Thomson-CSF TH7866A Charge-Coupled Device, permits electronic shuttering which effectively varies the dynamic range over an additional three orders of magnitude. Communication with the NEAR spacecraft occurs via a MIL-STD-1553 bus interface, and a high speed serial interface permits rapid transmission of images to the spacecraft solid state recorder. On-board image processing consists of a multi-tiered data compression scheme. The instrument was extensively tested and calibrated prior to launch; some inflight calibrations have already been completed. For a detailed overview of the Multi-Spectral Imager and its objectives, design, construction, testing and calibration, see [HAWKINSETAL1997] Space Science Reviews 82, 31-100. The text in this data set catalog object has been extracted from this paper. Two major subassemblies make up the MSI instrument: a camera and a Data Processing Unit, or DPU. These two assemblies are physically separated by about 100 mm and are located on the aft deck of the NEAR spacecraft, with the camera's optical axis parallel to the X'-axis of the spacecraft. A refractive optical telescope, a filter wheel, and a detector with its associated electronics are all part of the camera. The DPU provides a digital interface to the spacecraft and supplies power and the master timing to the camera. Camera Assembly =============== The camera specifications are summarized here: Mass: Camera 3.7 kg DPU 4.0 kg Power: Camera 1.43 W DPU 5.49 W FOV 2.93 x 2.25 degrees Spectral Range 400 - 1100 nm Refractive Optics 5 Elements Focal Length 167.35 mm Clear Aperture (no cover) 18.6 cm^2 Clear Aperture (with cover) 4.35 cm^2 Frame Size 537 x 244 Frame Rate 1 Hz Frame Size (no compression) 1.6 Mbits Quantization 12 bits Exposure Control 1 ms to 999 ms Filter Wheel 8 Position Broadband ('Clear') 700 nm Green 550 nm Blue 450 nm Red 760 nm IR1 950 nm IR2 900 nm IR3 1000 nm IR4 1050 nm Data Processing Unit Assembly ============================= The MSI Data Processing Unit (DPU) provides the necessary digital interface to the camera's FPD, and houses all of MSI's power converters, filter wheel control electronics, and the master clocking required by the camera. A microprocessor within the DPU receives commands from one of the two redundant spacecraft Command Telemetry Processors (CTPs). The CTP distributes commands, collects data from all instruments, and formats the data for recording and downlinking. Communication with the spacecraft takes place via a MIL-STD-1553 bus or alternatively through a high speed serial link (2 Mbits/s). Eight image buffers within the DPU allow temporary storage of the image data, permitting a variety of data compression algorithms to be applied to the data. Implementation of a multi-tiered compression scheme allows any algorithm to be applied to the data individually, or in combination. Both lossy and lossless compression algorithms are available. Images acquired and digitized by the camera are transferred to the DPU in parallel through a short harness. A 1 Hz timing signal from the spacecraft synchronizes commands from the DPU to the camera. Integration times may be commanded from 1 to 999 ms, effectively varying the sensitivity of the instrument by nearly three orders of magnitude. Each full image is made up of 244 x 537 pixels and contains a header of all the parameters associated with the image, including the time the image was taken, CCD temperature, exposure time, filter, data compression information, etc. The data are packetized within the DPU. In addition to the image data, each packet also includes information to locate its data within the overall image. This design minimizes data loss in the event of a single lost or corrupted packet.